Field of the Invention
The present invention relates to a puncture-free inner tube having a hollow pipe shape that has a light weight with durability capable of preventing damages from occurring on countless contacts with an outer tire due to elastic deformation, and also has excellent ride quality.
Description of the Related Art
In the present specification, the “circumferential direction” of the tube or the divided tube means the direction along the outer contour in the transversal cross section thereof, and the “longitudinal direction” means the axial direction of the tube or the divided tube having a hollow pipe shape.
Known examples of a puncture-free inner tube, which is not punctured even though nailing, (which may be hereinafter referred simply to a “tube”) include the tube described in JP-A-2005-205885. The tube described therein uses a gelled elastic material formed by injecting a heat-melted resin in a tube for a pneumatic tire, to which air is to be injected, (which may be hereinafter referred to as a “pneumatic tube”), and then solidifying the resin by cooling. The tube suffers weight increase of approximately 1,300 g for a tire with a size (26×1⅜) in addition to the pneumatic tube (weight: 170 g).
The tube described in JP-A-2010-111378 is a single rod shaped material formed of a foamed elastomer having a length corresponding to a circumferential length of a tube, and is used by inserting the material in an annular space of an outer tire constituting a tire in such a manner that both end surfaces of the material are confronted with each other. The tube requires a spacer for filling a gap between the tube and a tire rim in a state where the tube is inserted in an outer tire, and thus suffers weight increase of 830 g as compared to a pneumatic tube. The weight increase of the tube is smaller than the pneumatic tube having a gelled elastic material filled therein described above, and thus achieves weight saving.
JP-A-2010-210930 describes a tube having a hollow pipe shape formed by molding an elastomer for reducing weight increase of the tube. The present inventors have filed JP-A-2012-236588 relating to a tube formed of a three-dimensional net formed into a rod shape, in which the three-dimensional net is molded to have elastic deformability by utilizing arbitrary entanglement of large number of resin threads formed of a thermoplastic resin. Both tubes shown above are used by deforming a material having a straight shape into an annular shape and inserting the material in an outer tire. The puncture-free inner tubes using a hollow pipe and a three-dimensional net require no pneumatic tube and suffer weight increase of approximately 680 and 510 g, respectively, for a tire with a size (26×1⅜), as compared to a pneumatic tube.
FIG. 20 is a table showing comparison of the four kinds of tubes shown above for “the material or shape”, “the weight”, “the necessity of a pneumatic tire”, “the necessity of a spacer” and “the weight increase”, and for “the material or shape”, the tubes are shown as “gel”, “foamed elastomer”, “pipe” and “three-dimensional net” in the order described above. The size of the tire, in which the tube is inserted, is (26×1⅜) for a Japanese city cycle, which is a versatile bicycle, and only for a tube of “foamed elastomer”, a spacer is used for conforming the tube to the tire shape in the transversal cross section.
In the development of a puncture-free inner tube, the three elements in properties and functions of the tube, i.e., the ride quality derived from the repulsive elasticity and the bending elasticity of the material, the durability, and the light weight, are essentially demanded and achieved simultaneously. The ride quality and the durability may be achieved by devising the material and the shape of the tube, but it is considerably difficult to achieve the light weight since it may contradict to the ride quality and the durability. Even though the tubes shown above achieve the demanded levels for the ride quality and the durability, they still have a problem of failing to achieve the light weight due to the too large weight increase from a pneumatic tube. In the bicycle industry as a major user of the tubes, it is recognized that the weight increase from a pneumatic tube is approximately 500 g for satisfying the light weight standard.
The present inventor experimentally produced a puncture-free inner tube C′ shown in FIG. 26A, which was reduced in weight by reinforcing a thin pipe 101 having a thickness of approximately 1 mm with a helical ribs R′ in both forward and reverse directions formed over the entire outer circumferential surface of the thin pipe 101, and subjected the tube C′ to a durability test. As shown in FIG. 26B, an outer tire 51 has a thickness that is gradually decreased from a ground part 57 toward a bead 54, and on acting a ground pressure thereto, both side part 58 connecting to the ground part 57 suffer the maximum deformation amount. As a result, it has been experimentally found that the tube C′ achieves the light weight standard, but in the durability test, as the side parts 58 connecting to both sides of the ground part 57 suffer the maximum deformation amount corresponding to the change of the ground pressure, the repeated deformation of the side parts 58 damages the portion of the outer tire 51 over the side parts 58 to an anti-ground part 59, and when the extent of the damage becomes severe, the aforementioned portion of the outer tire 51 is broken. In FIG. 26B, numeral 53 denotes a tire rim.